<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div{
            width: 100px;
            height: 100px;

            padding: 100px;
            background: red;

            border: 10px solid;
            margin: 50px;
        }

        a{
            width: 100px;
            height: 100px;
            padding: 30px;
            background: green;
        }
    </style>
</head>
<body>

<!-- 在css中 背景色=元素内容区域+内边距 -->

    <hr>
    <div>
        div
    </div>
    <hr>
    <a href="https://www.baidu.com">百度</a>
    <hr>

</body>
</html>
